The present invention relates generally to a method and apparatus for penetrating a sheet material web, and in particular, to a method and apparatus for penetrating a sheet material web, such as by slitting, cutting, puncturing or perforating, while the web is being carried on a fabric.
It is well known in the field of paper making, and particularly in the field of manufacturing tissue products such as facial tissues, bath tissues and paper towels, to provide an apparatus for longitudinally slitting a continuous running sheet material web into two or more strips. Typically, the sheet material web is slit either as it traverses an "open draw" before being wound into rolls, before it is dried or after it is wound onto the roll. In the first instance, the area of open draw, where the dried sheet is momentarily unsupported before being wound, provides an ideal place to slit the web. In particular, the slitting device, often configured as a rotary saw blade, can be applied to the web without concern about cutting or otherwise damaging an underlying fabric, which otherwise carries the sheet material web throughout the forming process. Fabrics of this nature can be expensive and difficult to replace.
However, as described in U.S. Pat. No. 5,591,309, issued Jan. 7, 1997 to Rugowski et al., and assigned to Kimberly-Clark Corporation, the same assignee as the present application, open draws are a frequent source of sheet breaks and associated production delays. As a result, tissue sheets often are designed to have high machine direction strengths in order to remain intact as they are pulled through the open draw. However, high machine direction strengths can adversely affect the quality of the web in terms of its desired softness. Therefore, as explained in U.S. Pat. No. 5,591,309, the elimination of open draws in tissue manufacturing can result in a sheet material being made more efficiently at less cost and with more desirable properties.
When the open draw is eliminated, the sheet material web is typically slit using a water jet prior to drying the web. However, such "wet slitting" can result in a degradation of the throughdrying fabric as it is exposed to hot air passing through the slit in the sheet material during the drying stage of the process. Moreover, the slit edges of the sheet material web may not dry evenly due to the pile up of fibers along the slit. Additionally, when the sheet material web is slit prior to drying, the various strips of sheet material web are difficult to control and can become inadvertently interwoven, or overlapped, as they are further carried towards the wind-up reel. Interwoven strips can be more easily damaged and can make the winding process particularly difficult. Moreover, adjacent rolls having interwoven webs can be particularly difficult to separate. Accordingly, the strips of sheet material web are typically required to be spread apart so as to prevent interweaving.
In contrast to slitting the web prior to drying, it is also known in the art to slit the sheet material web as it is wound onto the roll, as mentioned above. Slitting apparatuses of this nature typically apply a pressure or guide roller, or like device, to the outermost surface of the roll so as to thereby control the penetration of the slitting device. However, facial and bath tissues typically have low densities. Accordingly, it usually is not desirable, or even possible, to allow such a guide roller to contact the roll as it builds so as to thereby control the position of the slitter, and the penetration thereof. Moreover, the various strips are necessarily wound onto the same roll and must be rewound onto separate rolls after slitting in another manufacturing step if desired.
Alternatively, the sheet material web can be carried on two or more belts aligned side-by-side, wherein a slitting blade protrudes through the gap between the belts. The sheet material web can become caught or torn in the gap, however, and it is not possible to change the lateral position of the slitting device without reconfiguring the belts, which can be very expensive and time consuming. Moreover, the control of the belts, and the alignment thereof, can be difficult to maintain.